In this blog post, we will look at the definition and types of stem cells, and how their ability to differentiate into various cells can lead to medical innovation.
Stem cells are also called liver cells or mother cells. All these names imply that they are cells capable of developing into any type of tissue. Thanks to this potential, stem cells offer innovative possibilities in the medical field, particularly in the treatment of incurable diseases and regenerative medicine, where active research is underway. In other words, stem cells are “undifferentiated” cells that have not yet differentiated. As such, they do not yet possess the characteristics of specific tissues, but under appropriate conditions, they can differentiate into various types of tissue cells. Stem cells are primarily obtained from embryos in the early stages of division and can be cultured into specific cell lines depending on the input provided. The term “stem cell” was first proposed by Russian scientist Maximoff at the Berlin Blood Society in 1908, and the existence of stem cells was finally proven by a research team at the University of Toronto in Canada in 1963.
Since then, stem cell research has expanded into various fields of life science and medicine, and scientists have delved deeply into the infinite possibilities of stem cells. Subsequently, in vitro fertilization and mouse cloning were successfully achieved in the UK and the US, and the birth of Dolly the sheep through somatic cell cloning marked the beginning of stem cells gaining significant attention. In 2004, South Korean scientist Hwang Woo-suk announced the successful cloning of embryonic stem cells using human eggs, but in 2005, an investigation revealed that the research data had been fabricated, causing a major scandal. This incident sparked global debates on bioethics and scientific responsibility, leading to more active discussions on transparency and ethical standards in scientific research. In 2013, a research team at Oregon Health & Science University in the United States announced that they had successfully cloned human embryonic stem cells, marking the first scientifically verified case of human embryonic stem cell cloning. This achievement marked a new turning point in stem cell research, and since then, stem cell research has continued to advance while overcoming various ethical and technical challenges.
There are several types of stem cells, including embryonic stem cells, adult stem cells, and induced pluripotent stem cells. Embryonic stem cells originate from fertilized eggs, which are formed when sperm (male reproductive cells) and eggs (female reproductive cells) combine. Embryonic stem cells possess the strongest differentiation potential, capable of developing into various types of body tissues, including nerve cells and heart cells. Typically, stem cells are harvested from the embryo on the fourth day after fertilization and cultured. They can also be isolated using somatic cell nuclear transfer. This method involves removing a cell from the body, isolating the nucleus containing the cell’s genetic information, removing the nucleus from an egg, and then inserting the isolated nucleus into the egg to culture it, resulting in embryonic stem cells with the same genetic information. Embryonic stem cells have the ability to differentiate into various types of cells, so they are also called pluripotent stem cells. This ability opens up possibilities for transplantation therapy but also carries the risk of tumor formation due to improper differentiation. They are easy to transplant because they do not cause immune rejection, can be mass-produced, and can differentiate into almost all types of body cells.
However, they have the drawback of being difficult to control differentiation, which increases the risk of becoming cancer cells. Additionally, they inevitably require egg donation and the destruction of embryos, raising significant ethical concerns. Adult stem cells, on the other hand, exist in extremely small quantities throughout the body. Unlike embryonic stem cells, which can differentiate into various types of cells, adult stem cells are cells that are already programmed to differentiate into specific types of cells that make up particular tissues.
As a result, adult stem cells are more suitable for therapies targeting the regeneration of specific tissues or organs compared to embryonic stem cells. For example, bone marrow cells are destined to differentiate into blood cells, while skin stem cells are destined to differentiate into skin cells. Adult stem cells do not require the destruction of embryos, making them ethically acceptable, and their differentiation is stable, eliminating the risk of becoming cancerous.
However, they have the major drawback of being able to differentiate into only specific cell types, are difficult to culture, and pose challenges due to immune rejection issues, making donation difficult. Induced pluripotent stem cells (iPS cells) are commonly referred to as iPS cells. These are stem cells created by reprogramming somatic cells to behave like embryonic stem cells, offering the advantage of being able to be derived from any part of the human body.
This technology holds great potential not only for treating specific diseases but also for genetic research and drug development. It is a groundbreaking achievement, as Japanese scientist Shinya Yamanaka was awarded the Nobel Prize in Physiology or Medicine for successfully achieving reprogramming. It is ethically unproblematic and the most medically promising type of stem cell.
Due to their ability to differentiate into any type of cell, stem cells are considered to have the highest medical value. Recently, there has been growing interest in the potential of regenerative medicine and personalized treatment, and stem cell technology is emerging as a core component of future medicine. And as stem cell research and stem cell therapy are actually being used clinically in blood diseases and treatment is being attempted in the field of neurology, stem cells are becoming closer to us and attracting attention not only in the medical community but also among the general public. In addition, experimental research on spinal cord injuries and various types of neurodegenerative diseases is being actively conducted both domestically and internationally.
Although stem cell therapy is currently underway, there is still a long way to go. This is because there are still numerous ethical and technical issues that need to be addressed before stem cells can live up to their reputation as a “dream therapy” for treating intractable diseases. Furthermore, discussions on the commercialization of stem cells are gaining importance alongside the establishment of social and legal frameworks. However, if research on stem cells continues, it is expected to bring about revolutionary advancements in both science and medicine.
